Track mounted lighting systems are commonly found in various health care examination and treatment facilities, such as medical and dental operations. See, for example, U.S. Pat. Nos. 3,936,671 and 4,975,817. See also, Track Light, Model 6300, offered by A-Dec, Inc., 2601 Crestview Drive, Newberg, Oreg. 97132.
In the latter, a ceiling-mounted track assembly is engaged by rollers carried by a trolley, on which is mounted a light post. The trolley and the light post are thus freely movable along the track assembly. Because of this free movement, the track assembly must be carefully installed and leveled. Otherwise, the trolley and light will tend to drift along the track. Also, when moving the light along the track from one position to another, the free movement of the trolley may result in over-travel, with movement terminated only by the trolley engaging stops at the ends of the track assembly.
As noted in U.S. Pat. No. 4,975,817, a freely movable carriage may be difficult to control, and may in fact, change position inadvertently, in response, for example, to building vibration. Spring-loaded friction pads may retard unwanted movement of a light bearing carriage, but they also render it more difficult to move, and of course, they must be adjusted, and eventually, replaced because of wear. As a solution to this problem, the ""817 patent proposes a system of opposed, spring-loaded brakes and a solenoid-actuated release mechanism. Here again, a brake system requires adjustment and eventual replacement of the brake pads, and a power or other failure of the solenoid release mechanism will result in the carriage being locked up against all movement.
It will be seen, therefore, that a need exists for a track light mounting system that is freely movable, yet is not susceptible to drift, over-travel, or other unwanted movement, and that will permit some tolerance in installation, but not rely on friction pads that must be adjusted and replaced or electromechanically actuated braking systems which are susceptible to lockups and other malfunctions.
The track mounted lighting system of the present invention utilizes hard, concave rollers in engagement with a complementarily shaped track, which in itself, is known, for example, in the Model 6300 Track Light noted above, but in accordance with the present invention, in combination with relatively soft, convex rollers, which exert a light frictional resistance, just sufficient to inhibit drift, over-travel, or other inadvertent movement of the lighting carriage along the track system.
Specifically, the track mounted lighting system of the present invention utilizes pairs of hard and soft, concave and convex rollers, positioned along and engaging upper and lower surfaces of one of the tracks of the system, while individual, soft, convex rollers engage an upper surface of the other of the tracks of the system. The upper surface of the track engaged by the hard, concave rollers, is complementarily configured to the concavity of the concave rollers, as in the above-noted model M6300 Track Light, but the roller-track engagement is maintained by the relatively soft convex rollers, which pair up with the concave, hard rollers and engage the lower surface of the track.
While various materials are available from which the hard and soft rollers may be molded, it has been found that an acetal resin sold under the trademark DELRIN(copyright) functions well for the hard, concave rollers, while a urethane formulated to a Shore A durometer rating of about 75 to 95 is satisfactory for the soft, convex rollers, with the urethane having a Shore A durometer rating of approximately 80 functioning satisfactorily.
With this unique combination of hard and soft, concave and convex rollers, resistance to drift, over-travel and other inadvertent carriage movement is avoided, while still providing ease of intentional movement and resistance to side loads. Additionally, it has been found that noise incident to carriage travel in prior art devices is substantially reduced. This is accomplished without resort to the prior art expedients of friction pads or braking systems and their attendant disadvantages.
The above and other objects and advantages of the present invention shall become apparent from the accompanying drawings and the description thereof.